Your bag-in-box holds 5 gallons of syrup.

There are 128 ounces in 1 gallon. So, there are 640 ounces in 5 gallons.

Your soda fountain system will mix water and syrup at a 5 to 1 ratio.

Divide cup size by 6 for number of ounces of syrup used per cup.-- Example for 10 oz. cup: 10 ÷ 6 = approximately 1.7. There are approximately 1.7 ox. of syrup used per each 10 oz. cup.  

Divide oz. of syrup used per cup by 640 total oz.
      Example: 640 ÷ 1.7 = approximately 376

This is the estimated number of servings per 5 gallon bag in box (*excluding ice)